2013 Annual Report
1a.Objectives (from AD-416):
To determine, in cooperation with scientists from Texas AgriLife Research, Kansas State University (KS), Texas A&M University (TAMU), and West Texas A&M University (WTAMU), atmospheric ammonia and methane concentrations and emissions at commercial beef cattle feedyards, and to determine the effects of environmental and management factors on the emissions.
1b.Approach (from AD-416):
Ammonia emissions will be measured at several commercial beef cattle feedyards and dairies in Texas using open path lasers and a backward Lagrangian Stochastic model. Methane emissions will be measured from the retention pond and pen areas of feedyards using the same methodologies. Nitrogen and carbon balance will be determined based on chemical composition of diets, fresh feces, aged manure, and animal weight gain. Effects of environmental factors, pond chemistry, pen surface chemistry, and management factors on emissions will be monitored. A respiration calorimetry system will be used to measure enteric and metabolic methane, carbon dioxide, ammonia and hydrogen sulfide flux from cattle. These data have value for development, improvement, and/or verification for statistical and process-based models of ammonia and methane emissions. Potential methods to decrease ammonia emissions will be studied using lab-scale and small plot-scale studies. Ammonia emissions from pen surfaces treated with varying chemicals will be measured using flow through lab chambers or a static chember on feedlot plots.
Three respiration calorimetry studies were conducted to evaluate the effects of corn processing method and wet distiller's grain on enteric methane emissions from cattle fed finishing diets. Enteric methane emissions were 25% less when cattle were fed diets based on steam-flaked corn than when fed diets based on dry rolled corn. Replacing corn with 15 to 30% wet distiller's grains did not significantly affect enteric methane emissions when dietary fat levels were held constant. However, feeding diets containing 45% wet distillers grains increased enteric methane production by 30%. This information is currently being used by USDA in a tool to estimate greenhouse gas emissions from cattle systems.
Methane emissions from a commercial feedyard were estimated using open path laser spectroscopy and a dispersion model. Methane emission rates agreed with values in the literature, and showed that cattle fed high-concentrate diets tend to have lower methane emissions than cattle that consume forage-based diets. To improve estimates of methane emission from feedyards, dairies, and pastures, two eddy covariance systems and a motorized scanning mount for an open path methane laser are being tested.
Accurate and user-friendly models are needed to predict ammonia emissions from livestock operations and to evaluate mitigation strategies. Because the quantity of ammonia emitted from feedyards is highly dependent upon the quantity and form of nitrogen excreted by the animals, a meta-analysis was conducted to determine the relationship between dietary nitrogen intake and nitrogen excretion by beef cattle. Empirical models were developed to predict urinary and fecal nitrogen excretion by beef cattle. A database of ammonia emissions from three commercial feedyards was used to develop regression equations to estimate ammonia emissions using environmental temperature, and dietary crude protein content. These simple equations can be used to improve estimates of ammonia loss from beef cattle feedyards and can be used in larger models to improve estimates of ammonia emissions.
Two existing process-based models, Manure-DNDC and the Integrated Farm System Model (IFSM), were evaluated for their ability to predict ammonia emissions from cattle feedyards. The predicted emissions made by both models agreed well with emissions measured at two feedyards, indicating that these models could be used for reporting ammonia emissions and to evaluate the effects of management practices and mitigation strategies on feedlot ammonia emissions.